The invention relates to a method for the making of heteroepitaxial layers, more precisely, a method for the making of at least one thin layer of a semiconductor material on a semiconductor substrate of another type.
The invention relates to the field of "thin layers" and, particularly, to the field of monocrystalline thin layers epitaxially grown on a substrate of a different nature.
The invention will be preferably applied to the growing of GaAs layers on Si, and it enables the removal, by blocking, of the dislocations generated at the crystal/substrate interface.
During the heteroepitaxial growth of GaAs on Si, dislocations are generated at the crystal/substrate interface and spread in the thin layer during the deposition. Very broadly speaking, the presence of these dislocations is due both to the difference between the lattice parameters of Si (0.54 nm) and GaAs (0.56 nm) and to the difference between their coefficients of thermal expansion (2.3 10.sup.-6 .degree. C. for Si against 5.6 10.sup.-6 .degree. C..sup.-1 for GaAs).
These dislocations once nucleated are practically impossible to eliminate during a normal growth of the MBE (Molecular Beam Epitaxy) or MOCVD (Metal Organic Chemical Vapor Deposition) type, thus considerably limiting the application of the heteroepitaxy of GaAs on Si.
For, since the dislocations act as recombination centers, they drastically reduce the lifetime of the minority carriers The result of this is that it is practically impossible to make bipolar components, such as lasers and photodiodes for example, in the heteroepitaxially grown layers of GaAs.
A method of blocking dislocations has been developed (see the French patent application No. 88 044 38 filed on Apr. 5, 1988). This method can be used to obtain practically fault-free dislocations. The principle of this method (known as the forced growth method) is shown in FIG. 1. One of the drawbacks of this method is that it calls for the use of two dielectric levels and two masking levels to make the seeding bands, on the one hand, and the bands enabling the access of the gas of the forced epitaxy phase, on the other hand (see FIG. 1).
The present invention enables the above method to be considerably simplified by limiting it to a single dielectric layer and to a single masking level.